The present invention relates to selectively colorable polymerizable compositions and to a method for forming selectively colored polymeric bodies using such compositions.
A selectively colorable solid object is an object that can be colored at small individual, but specifically defined, sites by irradiating light of a particular wavelength and specific intensity for a specified duration. The light sources capable of producing the selectively colorable solid object include: (a) a laser interfaced with an XY scanner (for polymer films), (b) a laser interfaced with an XYZ scanner (for 3D parts), (c) digital mirror device, (d) UV and Visible lamps with a masking device, etc.
A selectively colorable resin (SCR) system consists of: (a) the matrix (a blend of polymerizable material or a solid polymer), (b) a color former, (c) a color initiator (species that generate other species capable of reacting with color former; may not be needed in some systems); and (d) a chain reaction initiator (radical or cationic or none depending on the system).
The conventional method for forming a colored plastic body is to add a dye or pigment to the liquid prepolymer composition. The composition is then cured with actinic radiation. The latter requires that the absorption spectra of the photoinitiator and the dye/pigment differ. If the dye/pigment absorbs actinic radiation at the same wavelength as the photoinitiator, slower or no cure will be achieved. The color formation method is also not selective. The entire plastic is uniformly colored. Still another problem is that the photopolymerization process requires actinic radiation, but the color forming process requires only that the composition be well mixed. Though one of the processes can be controlled by the intensity/wavelength of the actinic radiation, the other is unaffected by it. Thus there is no selectivity of color formation in the plastic body.
Accordingly, there is a need for selectively colorable polymerizable compositions and for a method of forming selectively colored polymeric bodies using such compositions wherein the colorization process can be controlled as to the location and intensity of the color formed.